A washer is a piece of hardware that is traditionally used to distribute the load of a threaded fastener, such as a bolt. One particular type of washer may additionally be used to indicate the preload on the fastener used to join structural members. The preload on a fastener is the tension created in a fastener when it is tightened. The tension on the fastener creates a compressive force in the joint known as a clamping force. One type of preload washer has bumps that flatten when a certain preload is reached. Another type of preload washer has silicone that squirts out of grooves in the washer when a certain preload is reached.
Measuring of the load present at the joints of structural members is beneficial in areas of manufacturing, such as aerospace. Therefore, it is desirable to design and use improved load-indicating washers.